Got a '96 AT with 165K on the odometer. And well, this hasn't been the best year for my Maxima. First there's a torn CV boot. Then it began stalling at stops, which turned out to be a failing MAF. And now it looks like I'm having some kind of voltage/current issues.

The first thing I noticed was the dash dimming briefly when pressing the brakes. It was very subtle, but still noticeable. I checked the battery voltage and everything seemed okay. A few days later I start the car and I see the brake light is on, and the dash dims even more when tapping the brakes (with the car running). After some driving the brake light turned off.

Next day the same thing happened. This time I tested the electrical load while idling by rolling down all windows simultaneously. The dash dimmed a lot, and the engine bucked a bit, too.

Next day, no problems.

The battery terminals are all clean. Here are the voltages, measured at the battery:

Off: 12.5V
Engine off, key at 'on': 12.4V
Idle: 13.4-13.7V
Revving: 13.84V

Is this an alternator going bad? Something else?

Edit: Something else I noticed... Things sounds a little... clunkier around the pulleys than they should:
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I would suspect so. I would suggest checking the alt. main harness for issues. I've seen the wiring coming from the alt corrode. However having low voltage to sensors may have been your issue to start with. If you have access to a shop or place that can show you the alt diode matrix. and See whats its actually doing, is what needs to be done. Go have it checked

 

The voltage reading while the engine is running is a bit low, below specs. Spec is 14.1 to 14.7.

A good alternator will not change voltage between idle and higher rpm.If you turn on everything on the car, then you might see a tenth difference between idle and revving.

 

I tested it some more and now it's idling close to 14.0V, but I switch on the headlights it dips to 13.5 before making its way back to 13.9V after 2 seconds. So it seems to me like the alternator can't provide the current in time, and the battery is coming in to pick up the slack.

 

A few more tests today. I ran the car with an old, nearly-dead battery (it only started with the help of a good battery in parallel). Everything behaved the same -- voltage at idle was about 13.5, revving to 13.8V. The engine didn't come close to stalling, so it doesn't look like the battery is picking up the slack, because this battery had barely any juice in it to begin with.

I'll examine the alternator connections a little later, maybe some the wires have comes loosed or become corroded and aren't carrying enough current through.

 

Your alternator has problems. The headlights only draw 8 -10 amps, less than 10% of the alternator's capacity. If the voltage dips like that, the regulator is having a problem.

 

Beat me to it. When an ALT goes bad, like 90% of the problems are due to the internal regulator.

 

Yeah, that's what I was figuring, so I already ordered a new alternator earlier today. I'll update this thread in about a week with results.

 

been driving my max for 3 weeks with the battery/brake light popping on like once a week. as soon as i turn off the max and let it sit for even 2 minutes, the lights go off. i wonder how long the alternator will last or if it's something else.

 

Have you considered keeping your voltmeter hooked up while you are drivinf so that you can monitor the voltage?

The specs for the alternator output voltage is 14.1 to 14.7 volts.

 

Got the new alternator in today -- not the easiest of jobs. But the voltage is now a steady 14.3-14.5, regarless of engine RPM or whether accessories are on. So that's good.

The new alternator (A Remy 90511 from RockAuto) seems a little whiny though. As in, I can hear it in with the hood open. The old one (OEM) didn't do that. I wonder if that's there to stay or if it goes away over time.

Also, there was a little bit of smoke from the work area when the engine warmed up, but it's probably just the gunk I rubbed off on the engine while working.

All in all, replacement alternator seems to have resolved the voltage problems.

 

yep, aftermarket alty's whine. comes and goes with mine, usually starts after i get her warmed up and then let her sit at work. been doing that for 5 years!